The lifting arm arrangement according to the present invention is used in connection with a pipe handling machine for lifting pipes from a horizontal position to a vertical position. When the pipes are in the horizontal position, they can, for example, be placed on a loading unit or stacked in a pipe store or the like.
When the pipes are brought into the vertical position, they are in a pipe stacking position and can then be put together to form a drill string. The individual pipes are thereby made up into stands that are stored in the vertical position in a suitable area on the drill floor. The stands are moved from this storage area to a well center as required, either when a drill string is to be made up or in connection with drilling when there is a need to extend the existing drill string with additional stands.
The lifting arm arrangement according to the present invention may be secured to a vertical column structure and can, for example, be secured to one or more carriages that are moved in a vertical direction along the vertical column structure in order to raise and lower the lifting arm arrangement.
The lifting arm arrangement according to the present invention can also be equipped with a pipe handling head that is used to grip around the pipe when it is to be lifted from a horizontal to a vertical position. The pipe handling head is secured to one end of the pipe stacking tool. The other end of the pipe stacking tool is connected to a gripper head, which is in turn mounted on a gripper head arm that is arranged to mount to the vertical column structure. The gripper head arm is able to move the gripper head relative to the vertical column structure in the horizontal direction.
Relatively large forces act on the pipe handling head when the pipe handling head grips around the pipe and lifts it from its horizontal position. These forces are transferred as torque forces to the gripper head. In the lifting process, one pipe end is firmly held by the pipe handling head, while the other pipe end hangs down so that the pipe has an inclination. The loading unit may then come to push against the hanging end of the pipe. This is a situation in which major forces will act on the pipe handling head and where the forces will be transferred as torque forces to the gripper head.
A problem in existing embodiments is that the gripper head is subjected to major torque forces when the pipe handling head is loaded, and the equipment thus sustains damage or is rendered ineffective as a result.